Nitrogen dioxide is one of the most ubiquitous and damaging of the world's pollutants. Our aim is to provide data that rationalize and predict the reactions of NO2 with the types of molecules that are potential targets when animals breath NO2-containing polluted air. In this proposal we describe 7 specific research projects. (1) We will continue our study of the products formed when cyclohexene (a simplified model of a cis-unsaturated fatty acid) reacts with NO2. We have reported a complete product analysis in organic solvents. We now propose a study of cyclohexene in an aqueous micellular system and ask: What is the effect of an aqueous solvent on the product mixture? We also ask: What is the fraction of NO2/N2O4 that reacts with water, dismutating to form nitrite and nitrate ions, and what fraction reacts with cyclohexene? (2) We will study the reaction of NO2 with unsaturated fatty acid esters in organic solvents to determine the fraction of the NO2 that reacts by addition to the double bond versus the fraction that abstracts an allylic hydrogen atom. (3) We will determine the structure of all of the products formed when methyl oleate reacts with NO2 in organic solvents. Analysis will use state-of-the-art GC-MS. (4) We will use kinetic methods to ask: What fraction of NO2 reacts with polyunsaturated fatty acids (PUFA) in an aqueous micellar system and what fraction reacts with water? (5) In the same system used in section 4, we will ask: What fraction of the NO2 reacts with PUFA by addition versus hydrogen-atom abstraction? (6) We will use stopped-flow kinetics to measure the absolute rate constants for reaction of PUFA, tocopherol and other antioxidants, thiols, and amino acids with NO2. (7) We will use stopped-flow kinetics to determine the absolute rate constants for the reaction of NO2 with polynuclear aromatic hydrocarbons (PAH). We have already reported a study of the relative rates of these reactions, but mechanistic complexities require the knowledge of absolute rate constants.